The following is not an admission that anything discussed below is part of the prior art or part of the common general knowledge of a person skilled in the art.
There are many applications for bitumen (which can also be referred to as asphalt). For example, asphalt may be used for waterproofing products or articles, such as roofs, buildings, boats, shingles, roofing felts, roofing sheets or roofing membranes, as well as for paving roads.
Asphalt shingles are generally the primary roofing materials for residential graded roofs. Asphalt shingles may comprise either organic felt materials or glass fiber reinforcing mats which are saturated or encapsulated with bitumen or asphalt to make them waterproof. In general, asphalt shingles are for steep slope roofing whereas modified bitumen membranes are for low slope roofing.
Asphalts for using in roofing applications have different requirements than asphalts for using in roads. Road asphalts typically fail due to low temperature cracking, repeated loading that can result in rutting and fatigue cracking, and water penetration that can result in physical damage due to repeated freeze/thaw cycles. In contrast, roofing asphalts typically fail due to thermal shock caused by repeated heating and cooling cycles, low temperature cracking and loss of aggregate due to flow.
When used in roofing applications, conventional asphalt compositions obtained through oxidation of asphalt which meets ASTM-D-946, ASTM-D-3381 or ASTM D-6373 specifications have limited flexibility and weatherability, causing early failure of roofing shingles. Accordingly, while similar parameters may be used to classify a roofing asphalt and a paving asphalt, e.g., penetration, viscosity, softening point, and the like, the specification for a paving asphalt is different to the specification for a roofing asphalt.
Using a particular crude oil, only certain grades of asphalt may be obtained. The asphalt grade which may be obtained will depend, inter alia, upon the processes used to prepare the asphalt and the additives which are included.
One additive that has been suggested for use in the preparation of asphalt is waste rubber products, such as tires or tubes. Incorporating waste rubber products into asphalt would allow the rubber to be recycled. However, there are a number of significant obstacles related to such use. Scrap tires contain different types of vulcanized rubber, for example polyisoprene, polybutadiene, styrene-butadiene, butyl, ethylene-propylene-diene, as well as fillers, plasticizers, surfactants and the like. Moreover, tires typically contain a significant number of different elastomers. Accordingly, waste rubber is not a single chemical compound but is a mixture of various compounds, the composition of which can vary from one tire to another.
Furthermore, because of the cross-linking of the polymeric material that takes place by the vulcanization process with sulfur or polymeric sulfur derivatives, ground rubber or crumb rubber does not disintegrate readily. The additional chemical bonds created during this vulcanization render impossible the complete dissolution of the polymer in hot bitumen, thus causing problems of stability of the material.
In addition, mixtures of bitumen and rubber are not homogeneous and form two phases of different density which are partially dispersed in one another. The system tends to decant and causes the upper layers, which have a lower density, to be constituted of polymer, while the lower layers, which have a higher density, are constituted of bituminous material. Therefore, if natural rubber or “polymers” are used, they will constitute part of the lower density layer and will thus accumulate at the surface. Crumb rubber, having a higher density (e.g., 1,200 kg/m3), will typically sink to the bottom of the reaction vessel. In cases where crumb rubber is used, the bituminous material will be part of a middle layer interposed between the polymer layer floating at the surface and the crumb rubber making-up the bottom layer.
Attempts have been made to mix bitumen with a wide range of polymers for various applications including roofing and paving. Such polymers include atactic polypropylene (APP) and styrene block copolymers (SBS) (e.g., styrene-butadiene-styrene (SEBS), styrene-isoprene-styrene (SIS), and styrene-ethylene-butadiene-styrene block copolymers (SEBS)). Unfortunately, it takes a relatively long time to process or dissolve the above-mentioned polymers in bituminous materials such as bitumen or various asphalt compositions. Further, these polymer modifiers can be degraded or aged by heat, UV light, weather or a combination thereof.
Attempts have also been made to mix rubbers such as ethylene propylene diene monomer (EPDM) with asphalts. See, e.g., U.S. Pat. Nos. 4,069,181; 4,738,997 and EP Patent Nos. 0338336 A1 ; and 0093500 A1. Additional rubber compositions are described in U.S. Pat. Nos. 3,873,483; 4,129,542; 6,414,056; U.S. Publication Nos. 2006/0243163; 2006/0249049; and European Application No. EP 0775719 A2. Unfortunately, the mixing often proves difficult.
U.S. Pat. No. 5,501,730 claims a process for producing a homogeneous asphalt composition. While these asphalt compositions may be suitable for various uses, it would be beneficial to provide a roofing asphalt composition having a longer life and improved weatherability.